Carbon Dioxide Absorption with Aqueous Potassium Carbonate Promoted by Piperazine

Abstract

This chapter presents thermodynamic and kinetic data collected for aqueous blends of piperazine (PZ) and potassium carbonate (K2CO3). Amine and potassium carbonate solvents have proven useful for the removal of CO2 from natural gas and H2. Researchers have shown that blending amines accelerates the absorption process. Mixtures of K+ and PZ have been investigated in a wetted-wall column at 40 to 80°C, typical conditions for an industrial absorber. The addition of 0.6 m PZ to 20 wt% (3.6 m) K2CO3 increases the rate of CO2 absorption by a factor of ten from the value in unpromoted solutions at 60°C. The addition of PZ increases the heat of absorption from 4 kcal/mol in 3.6 m K+ to 10 kcal/mol when 0.6 m PZ is added. The capacity, ranging from 0.4 to 0.7 mol- CO2/kg-H2O, approaches that of monoethanolamine (MEA) solutions and seems to be a strong function of K+ concentration. Speciation of the solution was obtained using proton nuclear magnetic reasonance (NMR), verifying and quantifying the presence of three PZ species. An equilibrium model and a rate model were developed to predict system speciation, equilibrium, and CO2 absorption rate. The model predicts that 3.6 m K+ increases the specific rate constant of PZ by a factor of five from its value in water. Piperazine is expected to accelerate absorption rates while K2CO3 retains a low heat of absorption. Also, the reaction of carbonate in bulk solution is expected to improve solvent capacity.